Both of my edge guides (mortising
jig and edge of stock
guides) must be adjusted for each new application; an
arbitrary setting is rarely right where you want it. The
adjustment can translate the cutter pathway centerline, facilitate
a pathway greater than the cutter diameter, or both. Translation
of the cutter centerline can be done with a setting change of the
edge guides or the guide rods can simply slide to a new location
within the casting. In the latter case, the 2 hold down
screws/knobs on the casting are loosened and the router is
relocated a measured amount.
It is customary & essential to start an edge guide cut with a
calibration cut. This is the case no matter what the edge guide
design may be. From the calibration (test) cut you can determine
how much the guide(s) or rods must be moved. If the guide(s) has
to be moved it can be translated as follows (without the accessory
below):

Slide the edge guide against the work and clamp the router
to the work. The router cannot move during the adjustment.

Select a spacer of a thickness = desired translation. For
example, if you'd like to move the cutter .25" away from you,
put said spacer between the work and the loose edge
guide. Then tighten the guide against the spacer. (A 1/4
drill, drill rod, gage block etc.)

The cutter will now reach .25" from where it was.

If the goal was to produce a .50" dado from 1/4" cutter, you'd
start with 2 edge guides against the work with a 1/4 spacer
between the work & one of the edge guides.
In this case the cut will probably start very near .50" but its
centerline may not be where you'd like it to be. In this event, we
have to move the router on its rods without changing the distance
between the edge guides.
To move the router (a measured amount) on its rods without
disturbing the edge guides:

Measure the distance between the subbase (or casting) &
one of the edge guides (inside). Whilst an adjustable parallel*
is the tool of choice here to get the inside measurement, a
caliper or rule can suffice.

Now loosen the casting screws to free the guide
rods. Subtract or add width to the parallel or create a scrap
cutoff equal in width to the change necessary (+ the initial
gap) to translate the centerline. E.g., if the cutter requires
a 3/8" translation and the initial measurement is 1.0" then
the spacer has to be 1-3/8" or 5/8" depending on which
direction you slide the tool.

Move the bugger against the spacer and lock the casting screws.

Adjuster (Product)

The new edge guide adjuster is designed to assist in making
the space adjustment between 2 edge guides for mortices, slots
etc. It can also be used to translate the cutter centerline when
only one edge guide is in play. Let's start with 2 edge guides
snug against a parallel workpiece. To open the cutter pathway (of
a mortise e.g.) you first measure the diameter of the cutter and
subtract that number from the desired width of the intended cutter
pathway. This number is duplicated with a spacer-feeler gage,
adjustable parallel, gage block, drill rod, sheets of "Post-it" or
whatever. Now you slide the acrylic adjuster up against one of the
edge guides separated by the spacer.
Lock the adjuster, remove the spacer, unlock the edge guide block
& slide it up against the adjuster. If you spent more than 1
minute on this adjustment you should report yourself to the
metrology police for disposition immediately.
The cutter pathway will be opened precisely by the amount of the
spacer. If the starting pathway is too wide, slide the adjuster
against the edge guide block and lock the two intimately
together. Now loosen the edge guide, place the spacer between the
guide & adjuster, and lock the edge guide. This maneuver shrinks
the cutter pathway exactly the amount of the spacer.

Tho not as sweet as an adjustable edge guide it is accurate to
.001", fast, simple to use, and low tech, nuthin' to break. The
12mm Acrylic blank is fully machined, deburred, flat and contains
2 non-marring all brass set screws. It is sized to overlap your
edge guide block and therefore will be easy to handle in
use.
One size does not fit all,however; you must dictate router model
number for the correct adjuster.

Ordering

1 unit: $24

2 units: $40

1 unit with an edge guide or mortiser: $18

2 units with an edge guide or mortiser: $30
(S&H inclusive with all 4 options.)